Over the years various types of pipe have been used in storm and sanitary sewer applications. Corrugated pipe is sometimes paved, at least in the floor of the pipe, to enhance the flow of water and increase the life of the pipe. Because of the corrugations in unpaved pipe, water does not drain entirely from the pipe resulting in its corrosion. Moreover, the bottom portions of the unpaved corrugated pipe would also deteriorate due to the abrasive action of sand and gravel flowing through the pipe. A coating of asphaltic or bituminous material internally covering a part or all of the corrugated pipe or linings of concrete, metal or other material were provided to facilitate hydraulic flow and to afford additional resistance to wear and corrosion at the bottom of these pipes. Such composite corrugated pipes were heavy and difficult to handle and were susceptible to breakage during handling.
U.S. Pat. No. 1,929,817 discloses a corrugated metal culvert having a metal tubular internal liner. The lined culvert was made by placing segmented blocks on the interior bottom of the culvert, inserting a sheet metal tubular liner within the culvert on the blocks and injecting a mass of material in plastic form, preferably asphalt mixed with crushed stone, between the culvert body and the liner. U.S. Pat. No. 2,081,872 discloses a corrugated culvert having a sheet layer of fibrous material resting on the inner crests of a corrugated pipe, a metal plate liner resting on the layer of fibrous material and bituminous material filling the spaces between the plate and the pipe. U.S. Pat. No. 2,746,090 discloses a paved pipe comprising a corrugated cylinder and asphalt material filling the spaces in the corrugation to afford a smooth internal surface. The paved pipe is made by placing a generally cylindrical form element inside a corrugated pipe, spaced from the pipe by a dam means, and pouring liquid asphalt between the form and the pipe. A parting substance, such as waterproof paper, may be used to protect the form from the asphalt. Since the disclosed process only paves a fraction of the pipe, the pipe may be rotated and paved several times until a totally paved internal surface is obtained. U.S. Pat. No. 3,550,639 discloses a buffer pipe for placing between metal pipes buried in the ground to absorb stresses. The buffer pipe has corrugations or bulges adjacent its opposite ends, the internal spaces of which are filled with fluid-impermeable sponge rubber to a point substantially level with the inside circumference wall of the pipe body. A neoprene rubber lining may be applied over the inside surface of the sponge rubber.
Thus while the prior art includes corrugated pipes with liners of various types, there still is a need for a corrosion resistant smooth-lined corrugated pipe that will find wide acceptance for use in storm and sanitary sewer applications.
There is also a need for a smooth-lined corrugated pipe that is lighter in weight than asphalt-paved, concrete-lined or metal-lined corrugated pipe.
There is in addition a need for a foam-filled, plastic-lined corrugated pipe that possesses toughness and corrosion resistance and is not susceptible to breakage during handling and installation.
Further, there is a need for a practical, reliable and economical method for producing such smooth-lined corrugated pipes.